Right, so, when I started reading the Martian I wasn't too massively interested in growing veg, I just did it and felt awesome when things grew. Now I know a tiny bit more, it strikes me as rather odd that your botanist can grow potatoes in a 10cm depth of soil. Potatoes (at least of the British variety) need a lot of depth. Just a thought

I could deepen the soil, though that would require him to have more water.

I might just stick with "botany powers" as an explanation, though. He mentions at one point that he can get away with a denser yield because he's carefully attending to each plant, while potato farms grow millions of times his crop size and have to let things progress naturally.

Well, since you mentioned there was trouble with his big water creation boom, I guess you have the opportunity to change the required water quantity if you want

I think the thing with potatoes (although I may have it completely wrong) is that your seed potato can be quite small, but the roots need space to create new potatoes. Also, when the plant is a few inches high you're supposed to pour a bunch of soil over the top of it, because that encourages potato growth rather than plant growth. Apparently.

However, I reckon you have the ability to hunt down a real life botanist and get their input

-A-

Having written this, it occurs to me that I have a whole department of Horticultural professionals just around the corner. I'll ask them